Wood treated for decay and insect resistance is typically used on building construction in applications particularly susceptible to wood destroying organisms. The most common application is for sills, which are generally the elongated wooden plates anchored to the tops of foundations to facilitate connection of floor and wall framing. These plates are generally 2″×6″ or 2″×8″ cross section pieces of treated lumber. In some applications two or more such plates are stacked to create thicker sills. Sills must, by all applicable building codes, be appropriately anchored to the foundations. The most common method of anchorage entails the use of anchor bolts, the unthreaded ends of which are embedded into the tops of foundation walls leaving the threaded ends projecting upwards above the walls. These anchor bolts are embedded at certain intervals along the horizontal length of the foundation wall, and the sills are drilled to provide holes which align with the bolts. The sills are placed over the bolts, and washers and nuts are applied and tightened to secure the sills to the walls.
The most commonly used wood treatment material is chromated copper arsenate (CCA). However, due to concerns about leaching of arsenic from the wood and the potential health hazards associated therewith, CCA is being phased out of usage for treating wood. Alternatives are known to be more corrosive to metal components used in conjunction with the treated wood. Corrosion of metal fasteners, such as anchor bolts and washers, presents an important issue of building integrity and safety. There exists then the need for means to protect metal fasteners from the corrosive effects of these chemicals.
Several kinds of metal protecting means have been employed or are being considered. Among them are fabrication of anchor bolts from corrosion-resistant alloys, painting impermeable compounds onto anchor bolts, and galvanic coating such as zinc. Corrosion resistant alloys are significantly more expensive than regular steel bolts. Painting materials on the steel bolts is only slightly more expensive, but highly subject to failure due to surface imperfections and scratches occurring in handling and assembly. Galvanic coatings are somewhat more expensive and will provide protection for a time period. However, these coatings work in a sacrificial mode to isolate steel from corrosion and their effectiveness will dissipate over time.
Thus there exists a need for a reliable method of protecting anchor bolt assemblies from corrosion arising from wood treatment chemicals.